(A) Field of the Invention
The present invention relates generally to a non-volatile memory with flash erase capability, such as electrically erasable programmable read only memory (EEPROM, hereinafter referred to as flash memory), and more specifically to a method for managing areas in the non-volatile memory that are defective.
(B) Description of Related Art
A flash memory such as a RAM (random access memory), a ROM (read only memory) or a hard disk is a device for storing data therein. The flash memory comprises a plurality of blocks and erase operations are performed on a block basis.
Each block of the flash memory is limited in the number of times the data therein can be erased. Thus, if the number of times a block of the flash memory has been erased exceeds the limited number of erasures as predetermined when it was manufactured, the concerned block turns bad or defective. A flash memory such as NAND flash memory may be manufactured with some bad blocks. Taking this into consideration, the manufacturer directs users how to find the bad blocks therein. When a read operation is performed in a block of a flash memory, data different from the data previously written in the block of the flash memory may be read. The presence of the bad blocks may cause troubles when reading the flash memory.
To avoid reading wrong data in the defect blocks, management information for the bad blocks is needed. This management information may be stored in separate memories such as a RAM or an EEPROM. However, when the management information is stored in the RAM, the information stored in the RAM may be entirely lost if power failure occurs during erasure of the flash memory. When the management information is stored in a separate memory such as EEPROM, the cost to construct a system increases, and the system is accordingly complicated.